The present invention relates generally to oil and grease seals for large trucks, semi-trailers and the like, and particularly to unitized seals having composite casings, i.e. one wherein the casings include both metal outer portions as well as plastic inner cups, particularly plastic inner cups with supporting or strengthening ribs, and stiffeners to which elastomeric bodies are bonded. The elastomeric body usually, but not always, includes a primary lip, a dirt lip and an excluder lip.
Such seals are generally unitized seals for heavy duty applications, such as on the wheels of trucks, tractors, semi-trailers and so on. The usual type of seal has a casing including an outer cup, which may or may not engage an excluder lip at its end, but almost always has one or more steps in its diameters. This outer casing or outer cup then also encloses a so-called inner cup which is crimped or rolled in position within the outer cup.
One diameter of the outer cup usually provides a wear surface for a primary seal lip and one or more auxiliary lips, all of which are formed in a separate piece and bonded to a stiffener. All these parts are held in place axially by the inner cup. Thus, the normal assembly contains an outer cup, an inner cup, and these entrap between them a seal containing at least a primary lip and a casing or stiffener of its own.
In this form of seal, either part can rotate. One part is securely fastened to a part that rotates and the other is affixed to a non-rotary part. The primary and secondary lips or primary and dirt lip seals are supported by a metal part or stiffener, whereas the outer casing serves as both the mounting flange and the wear sleeve for the combination.
In the past, there has been a large number of designs in which both components are made from metal; the wear sleeve and the inner cup. A few limited attempts have been made to form the outer cup from a plastic material. However, such attempts have always met with failure, primarily because the plastic cup or wear sleeve lacked the necessary stiffness and especially because it was not suitable for seating or being forced into the seal-receiving opening with the force required. When it was sized so as to be forced into the seal opening, it would usually collapse or otherwise be deformed, making it unsuitable for such application. If it were dimensioned with little or no interference, it would not seal properly. As the result of such efforts, attempts to make a plastic outer cup have uniformly met with failure.
On the other hand, such seals also contained an inner cup, which has different requirements from the outer cup, and yet no efforts have been made to form the inner cup from a plastic material. The present invention concerns making the inner cup from a plastic material, and particularly a plastic material which has a variety of supports or strengthening ribs throughout its circumference. In addition, the plastic inner cup may have an angular wall for additional support and to prevent excessive agitation of entrapped oil.
In some cases, the ribs or strengthening formations on the inner cup have notched out areas to prevent possible interference with various bearings or other components of the wheel hub mechanism.
Accordingly, there are considerable advantages to be had in this type of product by the use of a plastic material. For example, the component or the inner cup can be made with almost any type of coloring, because the color potential for plastics is relatively unlimited. Such a seal can easily have manufacturing identifications placed on it, such as the date of manufacture, the identification of the supplier and so on. These can be placed on the molded inner cup with readily changeable inserts. Needless to say, such parts can be made at reduced cost in relation to making them of metal. For example, also there are no troublesome sharp or cut edges characteristic of the inner metal cups of the prior art. Needless to say, the use of plastic would create greater design flexibility because of the ease with which a plastic inner cup can incorporate components such as magnets, tone rings, heat sensors, etc. which can be molded in place as an integral part of the inner cup, or added later. Consequently, an appropriate location could be reserved for such parts in the future.
The use of a plastic inner cup would simplify a complex method of manufacturing, create a potential for reducing noise, and have the potential of greatly reduced weight. Such an inner cup would avoid an abrasive contact with mating parts and thus reduce the amount of heat potential caused by rubbing a plurality of metal and rubber parts together. Complex shapes could be made in such an inner cup without the difficulties encountered in putting counterpart complex shapes in metal inner cups.
Consequently, it is an object of the present invention to provide a seal, particularly a unitized seal, having a metal outer cup combined with a plastic inner cup.
Another object is to provide a plastic inner cup which is strong but may be manufactured in a complex shape.
A further object of the invention is to provide a plastic inner cup for a heavy duty seal wherein the plastic inner cup contains a plurality of regularly spaced stiffening ribs or the like.
A still further object of the invention is to provide a plastic inner cup for complex seals which contains not only ribs, but which ribs are combined with cutouts or the like to clear various otherwise interfering parts.
A still further object of the invention is to provide a plastic inner cup thereby reducing the noise potential for such seals in use.
A further object of the invention is to reduce the weight of such seals, in view of the several times lower density of the plastic material compared to metal.
A still further object is to reduce manufacturing cost.
These and other objects of the present invention are provided by having a seal made from an outer cup having a complex contour and serving as a wear sleeve, an inner seal member including a steel stiffener or casing surrounded by a rubber member which serves as the primary seal, and a third member or inner cup made from a plastic material and secured in place within the outer cup, preferably having a plurality of evenly spaced stiffeners or ribs of various forms, including reinforcing ribs and/or notched ribs, on the plastic inner cup.
The manner in which these objects and others are achieved in practice will become more clearly apparent when reference is made to the following detailed description of the invention set forth by way of example and shown in the accompanying drawings in which like reference numerals indicate corresponding parts throughout.